The conversion of 17.alpha.-hydroxy steroid (I) to produce a corticosteroid (II) by addition of a peracid is well known to those skilled in the art. See U.S. Pat. No. 4,041,055, Col. 6, lines 35-67 and Col. 14, line 59 to Col. 15, line 20 et al.
The general method of conversion is to react the 17.alpha.-hydroxy steroid with a peracid and the corresponding ester alcohol and/or of the peracid is obtained as a corticoid product. For example, if the peracid is peracetic acid the 21-acetate of the corticoid is produced as a mixture with the free alcohol. See Example 17, U.S. Pat. No. 4,041,055, et al. However, that procedure yields less of the corticoid product 11.beta.,17.alpha.-dihydroxy-21-acetoxy-4,9(11)-pregnene-3,20-dione when 11.beta.,17.alpha.-dihydroxy-20-phenoxy-pregna-4,9(11),20-trien-3-one is reacted with peracetic acid. The advantage of the process of the present invention is a surprising and unexpected increase in yield of product and the ability to isolate the 20,21 epoxide.
20,21-epoxy-20-alkyl-pregnanes are disclosed in U.S. Pat. No. 3,998,829. See Col. 9, lines 1-4.
F. DiFuria, et al. in Pure & Appl. Chem., Vol. 54, No. 10, pp. 1853-1866 (1982) describe the mechanisms of the polar oxygen transfer from peroxo and metal peroxo species.
R. E. Montgomery in JACS, 96, 7820-21 (1974) reported that certain ketones catalyze a number of peroxymonosulfate ion (HSO.sub.5.sup.--) reactions in weakly alkaline solutions. See also U.S. Pat. No. 3,822,114.
J. O. Edwards, et al. in Photochemistry and Photobiology, Vol. 30, pp. 63-70 (1979) suggests the involvement of dioxirane intermediates in the ketone-catalyzed decomposition of peroxymonosulfate (Caroate) HSO.sub.5.sup.-. OXONE.RTM. (Dupont de Nemours) is described as a mixture of potassium peroxomonosulfate (Caroate), KHSO.sub.4 and K.sub.2 SO.sub.4 containing approximately 42% of the peroxide and ca. 4.5% active oxygen.
A. R. Gallopo, et al. in J. Org. Chem., 1981, 46, 1684-1688 reported the kinetics of the oxidation of pyridine by peroxomonosulfate ion catalyzed by acetone and cyclohexanone.
R. Curci, et al. in J. Org. Chem., 1980, 45, 4758-4760 described the epoxidation of alkenes by dioxirane intermediates generated in the reaction of potassium caroate with ketones and also reports the use of a catalytic amounts of 18-crown-6 and tetrabutylammonium hydrogen sulfate as phase-transfer catalysts.
S. N. Suryawanski and P. L. Fuchs in Tetrahedron Letters, 22, 4201 (1981) reported that a dienol ether could be converted to a .gamma.-hydroxy-.alpha.,.beta.-unsaturated ketone by reaction with KHSO.sub.5 in tetrahydrofuran, sodium bicarbonate and water.
H. Mimoun in Angew. Chem. Int. Ed. Engl., 21, (1982) 734-750 describes various selective oxygen-transfer reactions from inorganic and organic peroxides to organic substrates; including the proposed mechanism of generation of dioxiranes in the reactions of most organic peroxides.
None of the above references describes the application of peroxidation reactions to the synthesis of corticosteroids.